London: Roger Federer clinched the first singles medal of his career Friday when he won an Olympic marathon. Federer outlasted Juan Martin del Potro of Argentina in the semifinals, 3-6, 7-6 (5), 19-17 in 4 hours, 26 minutes. Federer converted only two of 13 break-point chances, the second coming in the next-to-last game. A four-time Olympian, Federer is assured of at least a silver. On Sunday he'll play in the...